1,4,4a,9a-Tetrahydroanthraquinone (hereinafter referred to simply as THAQ) is a compound which is useful as an intermediate for dyestuffs or as a raw material for anthraquinones and which has recently been used as a pulp digesting agent.
When THAQ is used as a pulp digesting agent, it is common to dissolve it in an aqueous sodium hydroxide solution, and use it in the form of such an aqueous solution. However, for the transportation of THAQ to the users, it is economical to handle it in a solid form.
However, as a result of a study by the present inventors, it has been found that THAQ, for example, a powder of THAQ, is likely to form undesirable lump solid very easily. For instance, when it was packed in bags in an amount of 25 kg per bag, and 10 such bags were piled and stored, whereby THAQ in the bags located at the lower portion of the pile solidified and formed a hard solid. Further, powdery THAQ has a drawback that a dust is likely to form when it is dissolved into an aqueous alkaline solution.
THAQ is usually produced by the Diels-Alder reaction of naphthoquinone (meant for 1,4-naphthoquinone unless otherwise specified) with butadiene (meant for 1,3-butadiene unless otherwise specified). However, it is chemically unstable such that it is susceptible to dehydrogenation by air or by light, or to enolization in the presence of a certain amount of an acid or base component to form 1,4-dihydroanthrahydroquinone or 1,4-dihydroanthraquinone. This tendency is particularly distinct in the case of THAQ obtained by using naphthoquinone for industrial purposes, as the raw material. Accordingly, in order to store or handle THAQ under a stabilized condition, it is preferred to mold it into pellets. For a molding method of THAQ, a patent application has been filed (Japanese Unexamined Patent Publication No. 9256/1979) for a method for molding by means of a flaker. However, in the method disclosed in this patent publication, particularly in the Examples thereof, the Diels-Alder reaction is conducted usually in the presence of an inert solvent such as o-xylene, and the method has a disadvantage such that unless the solvent is removed almost completely, for example, to a level of at most 0.1% by weight, from the reaction solution containing THAQ, the product is hardly moldable. Further, the solidification speed of the melt of THAQ, and the releasability of the molded product have been inadequate. Thus, with such a method alone, it has been practically difficult to practice the method on an industrial scale.